1. Field of the Invention
This invention pertains to a flashlight constructed with several redundant elements for long-term reliability and more particularly to a hand-held flashlight with a backup system which may be selectively activated when the primary electrical system has failed.
2. Description of the Prior Art
Flashlights, and especially hand-held flashlights are used in many instances as primary sources of light in locations which are situated too far for the use of light sources connected to an electric power distribution network, or in which locations the distribution network has failed. Frequently these flashlights, and especially the flashlights designated for emergency use only, are stored away for long time periods between activations. However the flashlights presently available are subject to failure even if they are not used frequently. Conventional flashlights usually have a single electrical system comprising one or more batteries which provide the power for the flashlight, a light bulb which generates the actual light beam, a switch for the selective actuation o the bulb, and interconnecting elements which provide the electrical path between these elements. All these elements are disposed in a common housing and the failure of any one of these elements results in the malfunction of the flashlight. For example, common batteries have a very limitted shelf life. After a relatively short time period has elapsed, these batteries are discharged even if they are not used. Furthermore the common batteries can produce various corrosive fumes which can degrade and ultimately cause the failure of the housing, the switch or the flashlight interconnecting elements. The switch is a mechanical device which is also prone to failure. Frequent activation of the flashlight causes a premature failure due to abnormal wear and tear of the contacts as well as metal fatigue of its components. If the switch is used infrequently, chemical action (due for example to fumes from the batteries as explained above)could cause the formation of non-conductive layers on the switch contacts. The useful life of light bulbs is affected by electrical shock caused an inrush current generated by the activation of the switch. The light bulbs are also affected by various mechanical shocks which are frequent when the flashlight is used in a rough environment. For example a flashlight bulbs frequently damaged when the flashlight is dropped. Finally the flashlight interconnecting elements are susceptible to long term chemical degradation as well as mechanical wear and tear.
In U.S. Pat. No. 4,333,129 a hand-held flashlight is disclosed in which two identical batteries disposed end-to-end are physically and electrically separated by a separator plate. Switching means are provided to couple the batteries in a common electrical circuit.
In U.S. Pat. No. 1,974,294 a device is disclosed comprising two separate flashlights connected by a hinge which allows the flashlights to be oriented either side-by-side to produce two parallel light beams or end-to-end to produce two beams directed in opposite directions.
In U.S. Pat. No. 3,299,262 a flashlight is disclosed which can be coupled to an external battery pack to provide a high intensity light beam if desired.
None of these references disclose a structure with the advantages described below.